Polarized push-pull electromagnetic unit and method of and apparatus for calibrating the flux thereof



M. R. HUTCHISON 1,774,920 LARIZED PUSH-PULL ELEC MAGNETIC UNIT AND METHOD OF AND APPARATUS FOR CA BRATING THE FLUX THEREOF File Jan 9 1929 Sept. 2, 1930.

N V E N T O R mllerjfeew fluid/E1430)! j Q'; ATTORNEY Patented Sept. 2, 1930 UNITED STATES MILLER REESE HUTCHISON, OF LLEWELLYN PARK. WEST ORANGE, NEW JERSEY, AS-

SIGNOR TO ECHODON, INCL, OF WEST ORANGE, NEW JERSEY,

DELAWARE PATENT. OFFICE A CORPORATION OF POLARIZED PUSH-PULL ELECTROMAGNETIC UNIT AND METHOD OF AND APPARATUS I FOR CALIBRATING THE FLUX THEREOF a imation filed .Tannary'9, 1929. Serial No. 331,344.

In the manufacture of electro-magnetic units of the push-pull type, such as are commonly employed in the cone and similar types of loud speakers for radio and phonograph '5 reproduction, considerable difficulty has been experienced in properly predetermining ,or calibratingthe magnetic flux of the permanent magnet.

This type of unit includes an armature pivoted bet-ween the pole pieces of a permanent magnet and elastically poised in equidistantly spaced relation to said pole pieces.

Associated with the armature are flat, oblong electro-magnetic coils adapted to be connected with the audio frequency circuit of a radio receiving set, acting when current passes through them to unbalancethe magnetic field and cause the armature to be rocked by the influence of the field.

It is a recognized fact that eflicient operation of such a unit depends in large measure upon very accurate predetermination of numher or strength of the linesof force that cut the armature. The spaces between the armature and the pole pieces must be very small, say aroundten-thousandths of an inch, and if the magnetic flux is too great the armature will tend to hunt on one or the other of the poles. On the other hand, if the flux is too weak, the power of the unit is seriously impaired.

Prior methods of attempting to accurately calibrate this magnetic flux are extremely slip-shod and haphazard, the most common practice being to originally saturate the permanent magnet and subsequently Weaken its magnetic qualities by wiping it with a stronger permanent magnet until the armature is finally balanced equidistantly beas conventional except for the magnetic shunt piece.

tween the magnet poles. I

In accordance with the present invention,

have devised a method of calibrating the magnetic flux with mathematical accuracy,

the calibrating method and apparatus being mately on the line 2 ment is directly proportional to the armature-cutting flux of the permanent magnet field. In carrying out the method, the coils are connected to a voltmeter and the armature oscillated through a predetermined range and at a predetermined rate of speed. The electro-motive force registered on the voltmeter will indicate whether the flux is above or below standard. Preferably the permanent magnet is originally. saturated and the voltmeter readings will always initially indicate an excessive flux which excess is gradually diminished by moving a magnetic shunt member'across the pole pieces of the permanent magnet to a point Where a voltmeter reading indicative of the standard flux is obtained. I Having thus calibratedthe flux, the shunt member is permanently set in its properly adjusted position.

I The use of the magnetic shunt piece not only facilitates original accurate calibration of the magnetic field,but serves as a magnetic keeper when the unit is in use. The keeper effect of the shunt materially reduces therate at which the permanent magnet tires and the shunt piece may be expertly readjusted, if desired, to restore the proper flux across the poles of a tired magnet.

The invention may be more fully understood from the following description in connection with the accompanying .drawings, wherein:

Fig. 1 is a top plan view of an electromagnetic unit operatively connected to the-calibrating apparatus with which the method is performed; and

Fig. 2 is a vertical sectional view approxi- 2 of Fig. 1.

The magnetic unit which I have illustrated Such a unit may include the permanent horse-shoe magnet 10 carrying the laminated pole pieces 11 which are of general U-shape in cross-section, with their backs against the legs of the magnet 10 and with their arms embracing the usual two pairs of fiat oblong coils 12 adapted to be connected in conventional manner to the audiofrequency circuit of a radio receiving set.

The usual non-magnetic straps 13 embrace the ends of the magnets 10, supporting the pole pieces 11 and the coils 12 and providing a mounting for the usual soft iron armature 14 which is pivotally supported between the pole pieces on laterally projecting trunnions 15 at its opposite edges." These trunnions permit the armature to rock about its center.

The distance between the armature and the pole pieces is very small, so small that an excessively strong permanent magnet will cause the armature to hunt toward one or the other of the pole pieces.

A novel feature of the present invention is the provision of a magnetic shunt plate 16, one end of which is connected by screw 17 to one of the straps 13 and the free end of which may be swung from the position of Fig. 1 inwardly toward the center of the armature to an extent limited only by the pushpull rod 18 connected to the top of the armature. As member 16 is swung inwardly about screw 17, more and more of the flux between the magnet pole pieces will be shunted through 16 and less lines of magnetic force will cut the armature 14.

One end of the push-pull rod'18 is connected to the upper end of a spring finger 19, the lower end of which is screwed or otherwise secured as at 20 to one of the straps 12. A connecting rod 21 is fixed at one end to the intermediate portion of the spring finger .19 andits other end is normally used to v1- brate the cone or diaphragm of the loud speaker. For purposes of calibration, however, it is-held by set screw 22 in a socket member 23 at one end of a flexible crank rod 24. Rod 2a is fixed to and projects radially from the strap 25 of an eccentric 26 keyed to a shaft 27which may be rotated from any suitable source of power (not shown). The coils 12 for calibrating purposes are electrically connected to a voltmeter 28. Such connections to the coils and the interconnections between the coils is the-same as when the device is used to operatet-he loud speaker.

In carrying out the method. shunt piece 16 is loose on screw 17, so that it may be readily manually turned about this screw as a center. The permanent magnet is saturated or overmagnetized. "he armature 14 is connected as above described. to the shaft 27 in such a manner that rotation of the shaft 27 results in reciprocation of the push-pull rod 18 and consequent oscillation of the armatiire 14.

\Vith this apparatus, the speed of rotation of the shaft 27 and the throw of the eccentric are constant factors. the armature 11 being oscillated through a predetermined range. preferably less than the clearance spaces between it and the poles and ata predetermined rate so that the electro-motive force registered on the voltmeter 28 will be directly proportionzl to the magnetic flux passing through the armature.

'ith a small-throw eccentric, the oscillation of the armature will approximate a sine wave or pure frequency rate of change of velocity and the alternating electro-motive force generated thereby will approximate simple harmonic and can be accurately measured.

Having previously determined what this electro-motive force should be for a standard flux. it is a comparatively simple matter to shift the shunt member 16 in a clockwise direction until such time as the voltmeter shows an electro-motive force indicative of the desired standard flux.

The screw 17 is then tightened and the shunt plate 16 serves as a keeper between the magnet poles which acts in a well-known manner to retard the rate at which the permanent magnet tires.

In the event that the flux at any time falls below standard, the flux may be recalibrated, in most instances by simply shifting the shunt plate in a counterclockwise direction, and without the need of re-magnetizing the permanent magnet.

It will be understood that the showing of the eccentric 26 is merely for purposes of illustrating one means for giving the armature a vibratory movement of precisely predetermined frequency and amplitude and that other means may be employed for the same purpose. Moreover. the present showing is more or less diagrammatic. The indicated throw of the eccentric is made much greater than permitted by the indicated clearance between armature and pole pieces, in order to make it noticeable that this element is in the nature of a crank. It will be understood also that the rod 21 or the coupler 23 may be guided to prevent lateral vibration when the eccentric is running at the desired speed.

I claim l. A method of calibrating the flux of polarized push'pull electro-magnetic units of a loud speaker to a predetermined standard which includes the steps of mechanically oscillating the armature of such unit at a predetermined rate and through a predetermined distance. noting the electro-motive force produced in the coils of the unit by such oscillation and adjusting a magnetic shunt member across the permanent magnet poles until an electro-motive force indicative of the predetermined standard is reached.

2. A method of calibrating the flux of polarized push-pull magnetic units of a loud speaker which includes the steps of overmagnetiziug the permanent magnet thereof, mechanically oscillating the armature of the unit at a predetermined rate and through a predetermined range. noting the electromotive force developed in the coils of the tro-motive force'is reduced to ah amount indicative of a predetermined standard.

3. A method of calibrating the flux of polarized push-pull magnetic units of a loud s eaker which includes the steps of substantlally magnetically saturating the permanent magnet thereof, forcibly oscillating the armature of the unit at a predetermined uniform frequency and through a predetermined range, noting the electro-motive force developed in the coils of theunit, adjusting a magnetic shunt member across the poles of the magnet until the electro-motive force is reduced to an amount indicative of a predetermined standard flux through the armature and then setting the shunt member in properly adjusted position.

4. A method of calibrating the, flux of polarized push-pull magnetic units of a loud speaker of the character which include a permanent magnet, an armature rockably mounted between the pole pieces thereof and held in central position by the magnetic flux,

coils at opposite sides of the armature ada ted to be connected to the audio circuit 0 a radio receiving set and to unbalance the magnetic field when energized and a push-pull rod connected to the armature; which method consists in reciprocating the push-pull rod through a redetermined range and at a predetermine frequency, noting the electromotive force generated in the coils by the armature oscillation which is caused by such reciprocation and adjusting a magnetic shunt member across the permanent magnet poles until such electro-motive force reaches an amount indicative of a predetermined standard flux.

5. In a loud speaker, apparatus for calibrating the flux of polarized push-pull magnetic units including means to mechanically oscillate the armature of the unit through a predetermined range and at a predetermined frequency, means to indicate the electromotive force set up in the coils of the unit by such oscillation and a magnetic shunt adjustable across the oles of the permanent magnet to vary the ox passing through the armature.

6. In a loud speaker, apparatus for calibrating the flux of polarized push-pull ma netic units including means to mechanically oscillate the armature of the unit through a predetermined range and at a predetermined requency, means to indicate the electro-motive force set up in the coils of the unit by such oscillation and a magnetic shunt adjustable across the poles of the permanent magnet to vary the flux passin through the armature, the means for oscil ating the armature including means toreciprocate the push-pull rod of the unit.

7. In a loud speaker, apparatus for calisuch oscillation and a magnetic shunt adjustable across the poles of the permanent magnet to vary the flux passing through the armature, the means for oscillating the armature including means to reciprocate the pushpull rod of the unit, and comprising an eccentrio-operated crank rod operatively connect: ed to the push-pull rod.

Signed at New York, in the county of New York and State of New York, this 18th day of October, A. D. 1928.

MILLER REESE HUTGHISON. 

